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Encyclopedia > Lipid
Some common lipids. At the top is oleic acid and cholesterol. In the middle is a triglyceride composed of oleoyl, stearoyl, and palmitoyl chains attached to a glycerol backbone. At the bottom is the common phospholipid phosphatidylcholine.
Some common lipids. At the top is oleic acid and cholesterol. In the middle is a triglyceride composed of oleoyl, stearoyl, and palmitoyl chains attached to a glycerol backbone. At the bottom is the common phospholipid phosphatidylcholine.

Lipids are broadly defined as any fat-soluble (lipophilic), naturally-occurring molecules, such as fats, oils and waxes. Although the term lipid is sometimes used as a synonym for fat, fats are in fact a subgroup of lipids called triglycerides and should not be confused with the term fatty acid. They usually end with the suffix "-ol". The term is also used more specifically to refer to fatty-acids and their derivatives (including tri-, di-, and monoglycerides and phospholipids), as well as other fat-soluble sterol-containing metabolites such as cholesterol. Image File history File links Size of this preview: 790 × 599 pixelsFull resolution (1985 × 1506 pixel, file size: 35 KB, MIME type: image/png) self-made in chemdraw I, the copyright holder of this work, hereby release it into the public domain. ... Image File history File links Size of this preview: 790 × 599 pixelsFull resolution (1985 × 1506 pixel, file size: 35 KB, MIME type: image/png) self-made in chemdraw I, the copyright holder of this work, hereby release it into the public domain. ... Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable sources. ... Cholesterol is a sterol (a combination steroid and alcohol). ... Example of an unsaturated fat triglyceride. ... Oleic acid Oleic acid in 3D Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable sources. ... Stearic acid also called octadecanoic acid is one of the many useful types of saturated fatty acids that comes from many animal and vegetable fats and oils. ... It has been suggested that this article or section be merged into Palmitic acid. ... Glycerine, Glycerin redirects here. ... Phospholipid Two schematic representations of a phospholipid. ... Lecithin, also known as Phosphatidylcholine Lecithin is usually used as synonym for phosphatidylcholine, a phospholipid which is the major component of a phosphatide fraction which may be isolated from either egg yolk (in Greek lekithos - λεκιθος), or soy beans. ... ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... For other uses, see FAT. Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. ... Example of an unsaturated fat triglyceride. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... Example of an unsaturated fat triglyceride. ... OWNEDOWNEDOWNED ... General chemical structure of a monoglyceride. ... Phospholipid Two schematic representations of a phospholipid. ... Sterols, or steroid alcohols are a subgroup of steroids with a hydroxyl group in the 3-position of the A-ring. ... A metabolite is the product of metabolism. ... Cholesterol is a sterol (a combination steroid and alcohol). ...


Lipids have many functions in living organisms including nutrients, energy storage, structural components of cell membranes, and important signaling molecules. The smooth endoplasmic reticulum also processes these lipids, which store energy. Look up cell membrane in Wiktionary, the free dictionary. ... Lipid signaling refers to a number of cellular signal transduction pathways that use cell membrane lipids as second messengers. ... The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ...

Contents

Fatty acids and glycerides

Main article: fatty acid

Chemically, fatty acids can be described as long-chain monocarboxylic acids the saturated examples of which have a general structure of CH3(CH2)nCOOH. The length of the chain usually ranges from 12 to 24, always with an even number of carbon atoms. When the carbon chain contains no double bonds, it is a saturated chain. If it contains one or more such bonds, it is unsaturated. The presence of double bonds reduces the melting point of fatty acids. Furthermore, unsaturated fatty acids can occur either in cis or trans geometric isomers. In naturally occurring fatty acids, the double bonds are in the cis-configuration. In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... CIS usually refers to: Commonwealth of Independent States, a modern-day political entity consisting of 11 former Soviet Union Republics CIS is also an acronym for: Canadian Interuniversity Sport Cancer Information Service Carcinoma in situ Centre for Independent Studies Center for Immigration Studies Chinese International School Cisalpino Citizenship & Immigration Services... Trans is a Latin noun or prefix, meaning across, beyond or on the opposite side [of] . It is the opposite of cis, which means on the same side [of]. In chemistry, a double bond (or ring) not subject to free rotation in which the greater radical on both ends is... Cis-2-butene Trans-2-butene In chemistry, geometric isomerism or cis-trans isomerism is a form of stereoisomerism and describes the orientation of functional groups within the molecule. ...


Glycerides are lipids possessing a glycerol (another name for which is propan-1, 2, 3-triol) core structure with one or more fatty acyl groups, which are fatty acid-derived chains attached to the glycerol backbone by ester linkages. Glycerides with three acyl groups (triglycerides or neutral fats) are the main form of fatty energy storage in animals and plants. Glycerides are esters of glycerol and fatty acids. ... Glycerine, Glycerin redirects here. ... For other uses, see Ester (disambiguation). ... Triglyceride (blue: fatty acid; red: glycerol backbone) Triglycerides are glycerides in which the glycerol is esterified with three fatty acids. ...


An important type of glyceride-based molecule found in biological membranes, such as the cell's plasma membrane and the intracellular membranes of organelles, are the phosphoglycerides or glycerophospholipids. These are phospholipids that contain a glycerol core linked to two fatty acid-derived "tails" by ester or, more rarely, ether linkages and to one "head" group by a phosphate ester linkage. The head groups of the phospholipids found in biological membranes are phosphatidylcholine (also known as PC, and lecithin), phosphatidylethanolamine (PE), phosphatidylserine and phosphatidylinositol (PI). These phospholipids are subject to a variety of functions in the cell: for instance, the lipophilic and polar ends can be released from particular phospholipids through enzyme-catalysed hydrolysis to generate secondary messengers involved in signal transduction. In the case of phosphatidylinositol, the head group can be enzymatically modified by the addition of one, two or three phosphate groups, this constituting another mechanism of cell signalling. While phospholipids are the major component of biological membranes, other non-glyceride lipid components like sphingolipids and sterols (such as cholesterol in animal cell membranes) are also found in biological membranes. A biological membrane or biomembrane is a membrane which acts as a barrier within or around a cell. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... In cell biology, an organelle is one of several structures with specialized functions, suspended in the cytoplasm of a eukaryotic cell. ... Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. ... Two schematic representations of a phospholipid. ... This article is about a general class of chemical compounds. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... A biological membrane or biomembrane is an enclosing or separating tissue which acts as a barrier within or around a cell. ... Lecithin is mostly a mixture of glycolipids, triglycerides, and phospholipids (e. ... Chemical structure of sn-1-stearoyl-2-arachidonoyl phosphatidylinositol Phosphatidylinositol (abbreviated PtdIns, or PI) is a minor phospholipid component of eukaryotic cell membranes. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Hydrolysis is a chemical reaction or process in which a chemical compound reacts with water. ... A secondary messenger system (also known as a second messenger system) is a method of cellular signalling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change. ... In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in what is thought of as... Chemical structure of sn-1-stearoyl-2-arachidonoyl phosphatidylinositol Phosphatidylinositol (abbreviated PtdIns, or PI) is a minor phospholipid component of eukaryotic cell membranes. ... It has been suggested that this article or section be merged into signal transduction. ... General chemical structure of sphingolipids. ... Sterols, or steroid alcohols are a subgroup of steroids with a hydroxyl group in the 3-position of the A-ring. ... Cholesterol is a sterol (a combination steroid and alcohol). ...


A biological membrane is a form of lipid bilayer, as is a liposome. The formation of lipid bilayers is an energetically-preferred process when the glycerophospholipids described above are in an aqueous environment. In an aqueous system, the polar heads of lipids orientate towards the polar, aqueous environment, while the hydrophobic tails minimise their contact with water. The lipophilic tails of lipids (U) tend to cluster together, forming a lipid bilayer (1) or a micelle (2). Other aggregations are also observed and form part of the polymorphism of amphiphile (lipid) behaviour. The polar heads (P) face the aqueous environment, curving away from the water. Phase behaviour is a complicated area within biophysics and is the subject of current academic research. A liposome is a spherical vesicle with a membrane composed of a phospholipid and cholesterol bilayer. ... This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. ... Schematic of a micelle. ... Amphiphile (from the Greek αμφις, amphis: both and φιλíα, philia: love, friendship) is a term describing a chemical compound possessing both hydrophilic and hydrophobic properties. ... Polymorphism in biophysics is the aspect of the behaviour of lipids that influences their long-range order, i. ...


Micelles and bilayers form in the polar medium by a process known as the lipophilic effect. When dissolving a lipophilic or amphiphilic substance in a polar environment, the polar molecules (i.e. water in an aqueous solution) become more ordered around the dissolved lipophilic substance, since the polar molecules cannot form hydrogen bonds to the lipophilic areas of the amphiphile. So in an aqueous environment the water molecules form an ordered "clathrate" cage around the dissolved lipophilic molecule. An example of a quadruple hydrogen bond between a self-assembled dimer complex reported by Meijer and coworkers. ... Amphiphile (from the Greek αμφις, amphis: both and φιλíα, philia: love, friendship) is a term describing a chemical compound possessing both hydrophilic and hydrophobic properties. ... A clathrate or clathrate compound is a chemical substance consisting of a Greek klethra, meaning bars (in the sense of a lattice). ...

Figure 2: Self-organization of phospholipids. A lipid bilayer is shown on the left and a micelle on the right.

The self-organisation depends on the concentration of the lipid present in solution. Below the critical micelle concentration, the lipids form a single layer on the liquid surface and are (sparingly) dispersed in the solution. At the first critical micelle concentration (CMC-I), the lipids organise in spherical micelles, at given points above this concentration, other phases are observed (see lipid polymorphism). Lipid bilayer and micelle, from Nupedia. ... Lipid bilayer and micelle, from Nupedia. ... Phospholipid Two schematic representations of a phospholipid. ... This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. ... Schematic of a micelle. ... In chemistry, the critical micelle concentration (CMC) is defined as the concentration of surfactants in free solution in equilibrium with surfactants in aggregated form. ... Polymorphism in biophysics is the aspect of the behaviour of lipids that influences their long-range order, i. ...


Nutrition and health

Lipids play diverse and important roles in nutrition and health. Many lipids are absolutely essential for life. However, there is also considerable awareness that abnormal levels of certain lipids, particularly cholesterol (in hypercholesterolemia) and, more recently, fatty acids with trans fatty acids, are risk factors for heart disease amongst others. We need fats in our bodies and certain types in our diet. Animals in general use fat for energy storage because fat stores 9 KCal/g of energy. Plants, which do not require energy for movement, can afford to store food for energy in a less compact but more easily accessible form, so they have evolved to use starch, a carbohydrate, (not a lipid) for energy storage. Carbohydrates and proteins store only 4 KCal/g of energy, so fat stores over twice as much energy/gram as other sources of energy. Furthermore, lipids can be stored in an anhydrous form whereas carbohydrates typically cannot, which means that anhydrous lipid stores about 6 times as much energy per weight as hydrated carbohydrates. As an example, a typical 70 kg man would have to weigh approximately 125 kg if his energy stores were converted from triacylglycerol to glycogen. The Nutrition Facts table indicates the amounts of nutrients which experts recommend you limit or consume in adequate amounts. ... Hypercholesterolemia (literally: high blood cholesterol) is the presence of high levels of cholesterol in the blood [1]. It is not a disease but a metabolic derangement that can be secondary to many diseases and can contribute to many forms of disease, most notably cardiovascular disease. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid (or organic acid), often with a long aliphatic tail (long chains), either saturated or unsaturated. ... A trans fatty acid (commonly shortened to trans fat) is an unsaturated fatty acid molecule that contains a trans double bond between carbon atoms, which makes the molecule less kinked compared to cis fat. Research suggests a correlation between diets high in trans fats and diseases like atherosclerosis and coronary... Heart disease is an umbrella term for a number of different diseases which affect the heart and as of 2007 it is the leading cause of death in the United States,[1] and England and Wales. ... Starch (CAS# 9005-25-8, chemical formula (C6H10O5)n,[1]) is a mixture of amylose and amylopectin (usually in 20:80 or 30:70 ratios). ... Lactose is a disaccharide found in milk. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...


The baby formula brands Enfamil and Similac offer versions with lipids (DHA and ARA) added to the base formula. An infant being fed by bottle. ... An infant being fed by bottle. ... Docosahexaenoic acid (commonly known as DHA; 22:6(ω-3), all-cis-docosa-4,7,10,13,16,19-hexaenoic acid; trivial name cervonic acid) is an omega-3 essential fatty acid. ... Arachidonic acid (AA) is an omega-6 fatty acid 20:4(ω-6). ...


Types of Lipids

  • Fat - Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition. Although the words "oils", "fats" and "lipids" are all used to refer to fats, "oils" is usually used to refer to fats that are liquids at normal room temperature, while "fats" is usually used to refer to fats that are solids at normal room temperature. "Lipids" is used to refer to both liquid and solid fats. The word "oil" is used for any substance that does not mix with water and has a greasy feel, such as petroleum (or crude oil) and heating oil, regardless of its chemical structure.
  • Phospholipid are a class of lipids, and a major component of all biological membranes, along with glycolipids, cholesterol and proteins. Understanding of the aggregation properties of these molecules is known as lipid polymorphism and forms part of current academic research. They have two regions named as head and tail. Heads are hydrophilic while tails are hydrophobic.
  • Steroids - A steroid is a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion. Cholesterol belongs to this class.
  • Waxes - Fatty acids and an alcohol. They are more hyrophobic than fats. And they are the natural coatings for apples and pears.

For other uses, see FAT. Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. ... Phospholipid Two schematic representations of a phospholipid. ... In chemistry and biology, Steroids are a type of lipid, characterized by a carbon skeleton with four fused rings. ... Cholesterol is a sterol (a combination steroid and alcohol). ... Wax has traditionally referred to a substance that is secreted by bees (beeswax) and used by them in constructing their honeycombs. ...

References

  • Chapter 12 in "Biochemistry" by Jeremy M. Berg, John L. Tymoczko and Lubert Stryer (2002) W. H. Freeman and Co.
  • B. Alberts, et al. (2004) "Essential Cell Biology, 2nd Edition." Garland Science. ISBN 0-8153-3480-X
  • E. P. Solomon, et al. (2005) "Biology, 7th Edition." Thomson, Brooks/Cole.
  • "Advanced Biology 2 - Principles and Applications." C.J. Clegg and D.G. Mackean. ISBN 0-7195-7670-9
  • J. M. Seddon, R. H. Templer. Polymorphism of Lipid-Water Systems, from the Handbook of Biological Physics, Vol. 1, ed. R. Lipowsky, and E. Sackmann. (c) 1995, Elsevier Science B.V. ISBN 0-444-81975-4

See also

Wikimedia Commons has media related to:
Lipids

Image File history File links Commons-logo. ... Biochemistry (from Greek: , bios, life and Egyptian kēme, earth[1]) is the study of the chemical processes in living organisms. ... Essential fatty acids, or EFAs, are fatty acids that cannot be constructed within an organism from other components (generally all references are to humans) by any known chemical pathways; and therefore must be obtained from the diet. ... Lipid signaling refers to a number of cellular signal transduction pathways that use cell membrane lipids as second messengers. ... In chemistry, saturation has four different meanings: In physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amounts of that substance will appear as a precipitate. ... This article is about the chemical family of steroids. ...

External links

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  Results from FactBites:
 
Lipid Profile (189 words)
The lipid profile is a group of tests that are often ordered together to determine risk of coronary heart disease.
The tests that make up a lipid profile are tests that have been shown to be good indicators of whether someone is likely to have a heart attack or stroke caused by blockage of blood vessels (hardening of the arteries).
The results of the lipid profile are considered along with other known risk factors of heart disease to develop a plan of treatment and follow-up.
Screening: Lipid Disorders in Adults (556 words)
Rationale: The USPSTF found good evidence that lipid measurement can identify younger people at increased risk for coronary heart disease, that risk is highest in those with other risk factors, and that the absolute benefits of lipid-lowering treatment depend on a person's underlying risk of coronary heart disease.
The USPSTF makes no recommendation for or against routine screening for lipid disorders in younger adults (men aged 20 to 35 or women aged 20 to 45) in the absence of known risk factors for coronary heart disease.
Rationale: The USPSTF found good evidence that lipid measurement in low-risk young adults can detect some individuals at increased long-term risk of heart disease, but the absolute reduction in risk as a result of treating dyslipidemia in most people is small before middle age.
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